Mobility of arsenic in the sub-surface environment: An integrated hydrogeochemical study and sorption model of the sandy aquifer materials

International audienceGroundwater and aquifer materials have been characterized geochemically at a field site located in the Chakdaha municipality of West Bengal, India. Sorption experiments were also carried out on a sandy aquifer material to understand the mobility of arsenic (As) in the sub-surface environments. The result shows that the areas associated with high groundwater As (mean: 1.8 μM) is typically associated with low Eh (mean: −129 mV), and high Fe (mean: 0.11 mM), where Fe2+/Fe(OH)3 couple is controlling groundwater redox potential. Analysis of the aquifer material total concentrations showed the dominance of As (range: 8.9–22 mg kg−1), Fe (range: 3.0–9.7% as Fe2O3) and Mn (range: 0.05–0.18% as MnO) in the silt-/clay-rich sediments; whereas fine-/medium-sand rich sediment contains considerably lower amount of As (<8.1 mg kg−1), Fe (range: 1.6–3.9% as Fe2O3) and Mn (range: 0.02–0.08% as MnO). The acid extractable As do not correlate with ascorbate extractable Fe-oxyhydroxide, however Fe-oxyhydroxide is generally high in the sediments from low groundwater As areas. Chemical speciation computations indicated Fe(II), Ca(II), Mg(II) and Mn(II) to be at equilibrium (with respect to calcite, dolomite and rhodochrosite) or slightly over-saturated (with respect to siderite). These carbonate minerals may therefore participate to the As immobilization. The measured total organic carbon (1%) and groundwater temperature (26–32 °C) coupled with sorption studies strongly favors microbially mediated Fe(III)-oxyhydroxide reduction as the dominant mechanism for the release of As in the groundwater. Oscillations of As, Mn and Fe concentrations with depth reflected pCO2 oscillations consecutive to microbial respiration intensity

Flexible and free-standing films containing cobalt-doped nanocrystalline zinc oxide dispersed in polyvinylidene fluoride matrix: synthesis and characterization

Synthesis of free-standing flexible Co-ZnO/PVDF composite films is realized by sol-gel technique. Modulation of the optical and microstructural properties of the above composite films with Co-doped nanocrystalline ZnO loading in PVDF matrix was studied critically. Uniform dispersion of Co-doped ZnO in PVDF matrix was indicated by SIMS studies. Information on the bonding environment was obtained from X-ray photoelectron spectroscopy and Raman spectroscopy studies. A very strong peak at similar to 695 eV for core level spectra of F1s along with those for C1s, Zn2p and Co2p dominated the XPS spectra of the composite films. Presence of the predominant beta-phase of PVDF along with peaks related to ZnO nanocrystals in the poled sample was observed in the Raman spectra

Arsenic mobilization in the aquifers of three physiographic settings of West Bengal, India: understanding geogenic and anthropogenic influences

A comparative hydrogeochemical study was carried out in West Bengal, India covering three physiographic regions, Debagram and Chakdaha located in the Bhagirathi-Hooghly alluvial plain and Baruipur in the delta front, to demonstrate the control of geogenic and anthropogenic influences on groundwater arsenic (As) mobilization. Groundwater samples (n = 90) from tube wells were analyzed for different physico-chemical parameters. The low redox potential (Eh = -185 to -86 mV) and dominant As(III) and Fe(II) concentrations are indicative of anoxic nature of the aquifer. The shallow (100 m) aquifers of Bhagirathi-Hooghly alluvial plains as well as shallow aquifers of delta front are characterized by Ca 2+ {single bond}HCO 3 - type water, whereas Na + and Cl - enrichment is found in the deeper aquifer of delta front. The equilibrium of groundwater with respect to carbonate minerals and their precipitation/dissolution seems to be controlling the overall groundwater chemistry. The low SO 4 2- and high DOC, PO 4 3- and HCO 3 concentrations in groundwater signify ongoing microbial mediated redox processes favoring As mobilization in the aquifer. The As release is influenced by both geogenic (i.e. geomorphology) and anthropogenic (i.e. unsewered sanitation) processes. Multiple geochemical processes, e.g., Fe-oxyhydroxides reduction and carbonate dissolution, are responsible for high As occurrence in groundwaters

Arsenic ecotoxicology: the interface between geosphere, hydrosphere and biosphere [Editorial]

Although arsenic (As) has been known since ancient times as a powerful toxin, it was not before the end of the 20th century that the occurrence of As originating from natural sources has been reported in groundwater in different parts of the globe. However, the problem did not receive much global attention until the 1980s when the biggest As calamity in the world was first reported in the Bengal delta in Southeast Asia. This was the starting point for an exponentially widespread scientific, policy and public interest regarding environmental contamination by As